There is a global need for clean, efficient, inexpensive, reliable power generation. These systems have power requirements that range from milliwatts to hundreds of kilowatts, and include systems from small embedded sensors to motor vehicle power systems. Currently, these power requirements are addressed by a range of technologies that includes electro-chemical batteries, photovoltaic cells, thermoelectric generators, fuel cells, and internal and external combustion engines. These solutions, however, are oftentimes insufficient in a number of important aspects, including a low energy density (electro-chemical batteries), a dependency on an external primary energy source (photovoltaic and thermoelectric generators), high cost and complexity (fuel cells and Stirling engines), high maintenance (internal combustion engines) and high emissions (diesel and spark ignition internal combustion engines).
Internal combustion engines are the one of the most widely used sources for portable power generation. The most common form are Otto and Diesel cycle reciprocating engines which consist of a rigid combustion chamber within which combustion is initiated which then drives the displacement of a rigid piston. This piston is then coupled to a mechanical-electrical transducer which provides the electrical output. In spark ignition engines, the combustion is initiated by a spark or glow plug, while in diesel engines combustion is initiated through the compression of a gas into which fuel is injected.
There are a number of inherent disadvantages in the commonly used rigid combustion chamber and piston design. First, a tight, low friction seal must be maintained between the rigid combustion chamber and piston in a hostile environment which includes high temperatures, high pressure spikes, high vibration, abrasive chemicals and contamination. Satisfying these requirements often depends on special seals, close mechanical tolerances and high performance lubrication. Generally, the operational life of the generator system is determined by the compliance of these seals. As a result, the need to periodically change the lubricant incurs the inconvenience and expense of regular maintenance.
Second, the mass of the engine is dictated by the need to withstand and contain the explosive force and heat of combustion. This is typically achieved through the use of a combustion chamber bore out of a large piece of metal, accompanied by a piston constructed of a large, solid piece of metal. In addition to the increased mass of the system, there is a loss of overall system efficiency due to the need to move the pistons, and in the case of reciprocating engines, reverse its direction. Finally, the operational speed of the system is limited by the strength of the materials that move the piston assembly. Reducing the operational frequency results in larger combustion chambers and piston for a given output power, and, thus, heavier engines.
Third, the operational temperature of the system is often limited by the material used in the construction of the rigid combustion chamber and piston to a lower range than is desired for maximum efficiency and the reduction of resulting pollutants. In addition, seal friction and leakage also contribute to engine inefficiency and the increased emission of pollutants.
Fourth, the combustion chamber and piston assembly must be manufactured to close tolerances to provide a low friction, low-leakage seal which increases the cost to manufacture the engine.
This invention relates to devices for generating electrical power from the controlled combustion of fuels using Homogeneous Charge Combustion Ignition (HCCI) which avoids the need for a rigid combustion chamber and piston.
Increasing the frequency of the combustion process reduces the energy released per combustion which can be used to reduce the overall mass of the combustion system. However, the speed of spark and diesel-based combustion poses a limit on the overall operational speed of an engine. Homogenous Charge Combustion Ignition (HCCI) has been recognized as a new combustion mode for internal combustion engines which can operate at a much quicker rate. In addition, by increasing the compression ratio and burning at lower temperatures, it can improve efficiency and reduce undesired emissions. HCCI relies upon a lean and well-mixed air-fuel mixture that is compressed. A resulting spontaneous burn produces a flameless energy release in a large zone almost simultaneously. This operation is very different from the spark/gasoline burn or the compression/diesel burn. HCCI can thus be a basis for an efficient engine, like a diesel engine, but without the NOx or particulate emissions of diesel.
It is a principal object of this invention to provide a system that is reliable, easily maintained and has a low weight as compared to similarly rated conventional rigid piston engines.
A further principal object is to provide an internal combustion system that can operate at higher combustion temperatures than are possible with conventional engines to increase the efficiency of the system and reduce the emission of environmentally harmful combustion products.
Another advantage of the present invention is that many of parts responding to the combustion do not have to be machined to close tolerances and can be formed, at least in part, from component materials that exhibit low densities, good wear and heat resistance, and have favorable costs of manufacture while providing the capability to scale the system down in power output.
Yet another advantage of the present invention is that it can be used with a variety of different fuels.